The present invention relates to a press jacket (or a press belt) for a press device for the treatment of web-like material, such as paper webs, and particularly relates to the materials of which the jacket is comprised.
The invention relates in addition to a process and a device for the production of such a press jacket.
The preferred field of application of such press jackets is papermaking machines. The said press device with the press jacket may be a so-called extended-nip press, e.g.
according to U.S. Pat. No. 4,238,287 (FIG. 1) PA0 according to U.S. Pat. No. 4,552,620 (FIG. 5) PA0 according to DE-OS 32 35 468 (corresponding to GB 2,106,557 B) (FIG. 1) and PA0 according to VOITH publication "Mehrschichtband" (imprint P 4002 K/0197 K/Sh/Sro - received in the library of the German Patent Office on 26.7.1984) PA0 according to DE-OS 35 01 635 (corresponding to U.S. Pat. No. 4,625,376) (FIG. 6)
as known in conjunction with papermaking machines.
This press unit can, however,
also be a press roll with a loosely arranged press jacket in a so-called matt calendar. A press unit can also be implemented in conjunction with a press jacket shrunk onto a roll.
In connection with the aforementioned press units, known press jackets generally comprise a flexible jacket in which is embedded a so-called reinforcement fabric. This reinforcement fabric comprises so-called peripheral yarns, which extend in the direction of travel of the press jacket and are made of a material with a high modulus of elasticity, and so-called longitudinal yarns, which extend in cross machine direction and which give the press jacket the required stability of shape. The longitudinal and peripheral yarns generally form a textile fabric shell which is initially pre-fabricated in web form and is made endless by joining the web ends, and which is finally cast with the wear-resistant elastomeric material and then fixed thermally.
From U.S. Pat. No. 4,238,287 a press jacket of elastomeric material with embedded yarn-like reinforcements is known. This press jacket exhibits a layer of reinforcement yarns which are enclosed like a sandwich by two layers of yarns running at right angles thereto. To give the press jacket according to U.S. Pat. No. 4,238,287 the required strength, the layers of reinforcement yarns have to be vulcanized together.
The press jackets known until now--apart from the exception to be described below--have one thing in common:
Starting from a flat fabric-like reinforcement insert, which is endless because of the spirally wound peripheral yarns or is made endless by joining the beginning and the end, the press jackets are subjected to successive stages of work:
Pouring of elastomeric material onto one side of the endless reinforcement insert and, if required, smoothing of the resultant surface;
turning of the product formed so far;
pouring of elastomeric material onto the other side of the reinforcement insert, and if required, smoothing of the second surface with possible working-in of grooves and/or holes.
If present, the joint between beginning and end of the fabric jacket forms a certain weak point. Further, the pouring of the elastomeric material in two working steps is problematic, because then the elastomeric material comprises two layers. There is thus the risk that the bond of the two layers (for example because of inclusions) is imperfect and/or not sufficiently permanent. This is particularly the case when the two layers--cf. U.S. Pat. No. 4,238,287--are not held securely together by the reinforcement insert as the reinforcement insert itself is also multi-layer.
The task of the present invention is to improve such a press jacket in such that even during a long service life there is no risk that individual layers will detach from one another. It should, however, continue to be ensured that the reinforcement yarns are completely embedded with the elastomeric material. Furthermore, the press jacket should be capable of being manufactured in a simpler and thus cheaper way without this being associated with qualitative disadvantages.
This task is solved by the following combination of features.
Improvements of the press jacket stated above are as follows. The result has the particular advantages that a material layer which is homogeneous throughout is obtained and the strength of the press shell is defined on the basis of the tension between the longitudinal and peripheral yarns and is reproducibly determinable. Of particular advantage also, the wear of the reinforcement yarns is eliminated and the life of the press jacket (as according to VOITH publication P 4022 K or DE-OS 32 35 468 or U.S. Pat. No. 4,552,620) is not excessively shortened. The material layer of the jacket may also be cast multi-ply.
The process for the manufacture of the known press jackets has already been outlined above. The process is generally expensive and--as already mentioned--also not unproblematic in terms of strength.
DE-OS 18 984 discloses a process for the manufacture of an endless press jacket in which a woven armouring belt is tensioned on a cylinder and the press jacket itself is cast on as an endless jacket in helical form. The armouring belt lies flush with the internal wall of the press jacket and the belt is thus, on the one hand, susceptible to wear and, on the other, destructible externally in that the yarns of the armouring belt can be pulled outwards individually. A complete cross linkage or shrouding of the armouring belt within the elastomeric material does not take place.
The process-specific task underlying the present invention is to indicate a method for the production of a press jacket according to the invention with which, in particular as compared with the method known according to DE-OS 33 18 984, a press jacket can be manufactured which exhibits mainly orthogonally aligned layers of reinforcement yarns which are completely embedded in the jacket material, i.e. which are sufficiently covered with jacket material at the two function surfaces of the press jacket.
This process-specific task is solved by the process steps with the particular advantage that, by pouring in one uniform step, weak points between the individual layers and air inclusions are precluded from the very beginning.
The present invention also provides a device for the manufacture of the press jacket according to the invention or a device for the performance of the process for the production of such a press jacket.